[autofit] Fix 'multi' compilation.

* src/autofit/ft-hb.c: Decorate with `FT_LOCAL_DEF`.
Add ANSI boilerplate code for otherwise empty file.
* src/autofit/ft-hb.h: Include `compiler-macros.h` and `freetype.h`.
Use `FT_BEGIN_HEADER` and `FT_END_HEADER`.
Decorate with `FT_LOCAL`.

* src/autofit/rules.mk (AUTOF_DRV_SRC): Add `ft-hb.c`.
3 files changed